Multiple forms of glucocorticosteroid receptors in the neural retina of chick embryo,revealed by polyacrylamide gel electrophoresis

The glucocortiocoid receptors in the cytosol of neural retina of the 15-day chick embryo were analyzed by quantitative polyacrylamide gel electrophoresis. Maintenance of the triamcinolone acetonide (TA)-receptor complexes under conditions of electrophoretic analysis is dependent on temperatures not exceeding ?2 °C and is favored by low ionic strength, but is relatively insensitive to changes in pH between 5 and 10. Polyacrylamide gel electrophoresis in highly crosslinked Resolving Gels (15% crosslinking with N,N′-diallyltartardiamide) at low wattage and under temperature control at ?2 °C, allowed for detection and partial characterization of over 80% of the specific TA-binding activity of the tissue. One form of the glucocorticoid receptor, designated as complex II, was found to have a molecular weight (M_r) of 175,000. In addition, specifically bound TA was found in a multimillion M_r aggregate which was unable to enter gels of any concentration investigated and has been designated TA-complex I. The ratio of complex I/complex II increased with increasing gel concentration, indicating physical or chemical interaction between II and I. A polyacrylamide gel electrophoresis rerun of isolated TA-complex II gave rise to two smaller TA-binding species: Component B, of M_r 108,000 and component A, a relatively fast migrating molecule which could not be characterized under the conditions used. The ratio of $\text{B}\text{A}$ appeared constant and close to 2, suggesting that A and B may be significant structural elements of complex II. Polyacrylamide gel electrophoresis of isolated TA-complex I gave rise to component C of M_r 60,000, but not to components A or B. Components A and B associated to a large M_r complex, designated as I′, which was revealed to an extent directly proportional to gel concentration. Similarly, component C aggregated to I″, as evidenced at elevated gel concentrations. In conclusion, it has been possible to define by gel electrophoresis three of the molecular species (A, B, and C) that comprise the glucocorticoid receptor, and the possible relationships between them.